United were furious after the game, and indicated they would make a formal complaint to referees’ body Professional Game Match Officials (PGMO).
The Red Devils’ issue was around consistency, with two other penalties awarded in the game for holding offences.
Manager Michael Carrick described the decisions as “baffling”, confused that Attwell’s decision did not match an earlier spot-kick given to his side for a pull by Alex Jimenez on Matheus Cunha.
“So the Cunha one, he gives, the second one on Amad he doesn’t, which is, I think, almost identical, really, two hands on someone in the box, and they go over and they’re in control of the ball,” Carrick said.
“Massive moment and I don’t understand how you can give one and not the other – it’s crazy. It’s as obvious as you can get.
“It’s clear, if that’s what he believes is a penalty to start with then the second one has to be.”
Match of the Day pundit Alan Shearer agreed and said: “You should have given a penalty when you gave two like that. How on earth do you not give another one.”
The KMI Panel backed the Cunha penalty 5:0, stating that “Jimenez clearly pulls the shirt of Cunha in a non-footballing manner”.